Artificial sponge and method of making it



nied States Patent ARTIFICIAL SPONGE AND METHOD OF MAKING IT Harry A.Toulmin, Jr., Dayton, Ohio, assignor to The Commonwealth EngineeringCompany of Ohio, Dayton, Ohio No Drawing. Application March 16, 1953,Serial No. 342,751

16 Claims. (Cl. 128-296) necessary to insert a porous material intodifferent parts of the body for the purpose of bringing a therapeuticagent into contact with certain tissues and organs and/or for picking upfluids in a wound area, such as blood and exudates.

Surgeons have the problem of keeping the amount of blood present arounda surgical incision at a minimum since the blood impedes the surgeonswork. A common practice is to apply a coagulating agent such as thrombinto the area for the purpose of clotting the blood. This practiceinvolves various problems. If the coagulating agent is poured into theincision, it tends to interfere with the surgeons work almost as much asdoes blood itself, and if a clot is formed, it is quickly washed away.To avoid this, it has been proposed to soak a porous material of theappropriate size in the coagulating agent and then place the materialcarrying the agent, thrombin or the like, at strategic points within theincision. While this technique may facilitate the surgeons task, itpresents the difficulty that most available porous materials, such asconventional sponges, are not absorbable and assimilated by the body,which means that they must be removed before the incision is closed. Thevery act of removing a conventional sponge from the body often initiateshemorrhaging. On the other hand, real damage results if thenon-absorbable materials are not removed.

'One object of this invention is to eliminate these and other problemsby providing a new porous or sponge-like material having a large numberof intercommunicating cells or interstices, which may be cut intoconvenient swabs or packs, and which is absorbable and readilyassimilated by the human body without harmful effects so that if it isplaced in an incision, for example, the latter may be closed withoutremoval of the porous material.

Another object is to provide a new sponge-like material which may bedeliberately left within an incision in order to keep a constant supplyof therapeutic agent at a given point therein, as well as to precludehemorrhage occasioned by its removal. I

A further object is to provide a new absorbable, readily assimilatedsponge-like material which can be made economically.

A still further object is to provide a sponge-like material as describedand which can be subjected to sterilizing conditions without undergoingdamage.

Another object is to provide a new sponge-like material adapted to avariety of uses.

These and other objects of the invention are accomplished by providing asponge-like material comprising a dextran or a dextran derivative. I Thedextrans are high molecular weight polysaccharides comprisinganhydroglucopyranosidic units linked by carbon-to-carbon linkages some,and apparently 50% or more of these linkages being alpha-1,6carbon-to-carbon linkages. The dextrans may vary with respect to theirmolecular structural repeating alpha-1,6 to non-1,6 linkages ratios,molecular weight, sensitivity to water and osmotic pressure in liquids.

The dextran sponge of the invention, in its final form, is insoluble inwater. It may comprise a dextran which is initially insoluble in wateror one which is initially water-soluble but which has been renderedinsoluble in water by suitable chemical treatment.

One method of making the dextrans involves the steps of inoculating aselected nutrient medium with a microorganism and incubating the mixtureat the temperature most favorable to growth of the microorganism untilthe maximum of dextran is obtained, as may be determined by periodicallyprecipitating samples of dextran from the culture medium by the additionof alcohol or acetone to the medium, and drying and weighing thesamples. Suitable microorganisms are those of the Leuconostocmesenteroides and L. dextranicum types.

Using microorganisms of these types, the culture medium must containparticular nitrogenous substances, certain inorganic salts, and somesucrose, which may be either refined or crude, or which may be in theform of a sucrose-containing substance such as molasses. The requirednitrogen may be added to the medium in the form of commercial peptone,beef extract or other nitrogencontaining substance. If molasses is usedas the sucrose source, the quantity of nitrogenous compounds presenttherein may be suflicient to provide the nitrogen required by themicroorganism, so that the addition of other nitrogen sources may not benecessary. Salts such as dipotassium phosphate and sodium chloride arealso added. A specific example of a suitable nutrient is an aqueousmedium containing: 5-10% sucrose, 0.5% peptone, 0.2% dipotassiumphosphate and 0.1% sodium chloride. Other growth factor supplements,such as liver, yeast and malt extracts also may be included, forinstance at 0.5% concentration. The pH of the medium is preferablyadjusted to slightly on the alkaline side of neutrality, and productionof the dextran is favored by maintaining the medium slightly alkalinethroughout the fermentation period, which may be accomplished by theperiodic addition of alkali to the fermenting medium or by using anexcess of calcium carbonate in the medium. The time required for maximumdextran production will vary with the organism employed, the temperatureof the incubation, the concentration of sucrose in the medium and otherfactors. When the maximum of dextran has been formed, an equal amount ofalcohol or acetone may be added to the medium at a pH of 2.5 to 4.5 toprecipitate, or complete the precipitation of, the dextran in pure formand substantially free from occluded or absorbed bacteria, nitrogenousmaterials and inorganic elements. Any watermiscible aliphatic alcohol,such as methyl, ethyl or isopropyl alcohol may be used to precipitatethe dextran. In order to further purify the precipitated dextran, it maybe mixed with water and reprecipitated with alcohol at a pH of about7.0, the pH of the dextran-Water mixture being adjusted by means ofsodium hydroxide, for instance, prior to the reprecipitation. In someinstances, it may be desirable to reprecipitate the dextran severaltimes.

The final precipitate may be dried free of alcohol and' water, andreduced to particulate condition for use in this invention.

The dextran as obtained initially is a high molecular weight substancewhich may be soluble or insoluble in water, depending on. the conditionsunder which it is obtained and particularly the microorganism. Thedextran obtained using the microorganisms .Leuconostoc mesenteroidesB4120; L. mesenteroides B4144; L.

3 mesenteroides 8-523; and Betabacterium vermiforme B4139 (NorthernRegional Research Laboratory classification) are initially substantiallywater-insoluble and may be used as such in practicing the invention, orafter hydrolysis by means of acid or enzymatically to a lower molecularweight such that the dextran remains substantially water-insoluble. Onthe other hand, the dextrans obtained using'the microorganisms.Leuconostoc mesenteroides B5l2, B1l46, 3-119 and B4146 (NRRLclassification) are initially soluble in water and are insolubilized foruse as a sponge substitute in accordance with the invention. Forexample, the dextran may be insolubilized by treatment withformaldehyde, a water-insoluble dextran polyformal being produced. Orthe dextran may be converted to other water-insoluble or substantiallywater-insoluble derivatives, which may or may not be adsorbed andassimilated by the living body. For example, the dextran derivative maybe a calcium salt of dextran or a calcium salt of carboxymethyl dextranwhich may be absorbed safely and which also serve to facilitate bloodcoagulation. A method for the production of water-insoluble calciumsalts of dextrans is described in the pending application of L. .l.Novak et al., Ser. No. 281,505, filed April 10, 1952. The calcium saltsof car'ooxymethyl dextran, which is disclosed in the pending applicationof M. H. Hiler, Ser. No. 327,938, filed December 18, 1952, may be madeby similar methods.

Since the dextran may be water insoluble as obtained, or renderedwater-insoluble by appropriate treatment, and dextrans having a widerange of molecular weights may be used, the invention is not limited tothe method by which the dextran is obtained. The dextran may be preparedenzymatically in the absence of bacteria. For example, a suitablebacterium may be cultivated to obtain a dextran-producing enzyme whichis separated from the culture and introduced into a medium in whichdextran is formed by the action of the enzyme. Or the dextran may beobtained by bacterial conversion of 1,4 linkages of starch-deriveddextrins to 1,6 bonds of dextran. These various dextrans may be used insubstantially pure form and after sterilization, as such, or in the formof their water-insoluble or substantially waterinsoluble conversionproducts, when the sponge is intended for therapeutic use. The purityand sterile condition are less important in the case of sponges destinedfor household or industrial use.

The sponge-like material is prepared by dissolving or dispersing thewater-insoluble dextran or dextran derivative in a solvent or dispersingmedium which may be aqueous or non-aqueous, to obtain a product ofthick, creamy or latex-like consistency, and then treating the dissolvedor dispersed dextran or conversion product to induce inflation orfoaming thereof, followed by drying of the foam.

Various foaming or inflating treatments may be used. For example, thedextran solution or dispersion may be beaten vigorously to produce afirm foam which may be dried in circulating air under controlledhumidity conditions. According to other useful embodiments, the foamy orinflated condition of the dextran or conversion product may be broughtabout by treating the solution or dispersion thereof with immisciblevolatile solvents or liquids which, on volatilization, induce foaming ofthe mass. Another useful method involves the use of chemical agents suchas sodium bicarbonate, ammonium carbonate, ammonium carbamate, ammoniumbicarbonate, a mixture of sodium nitrite and ammonium chloride, and thelike, which evolve as a gas on heating. Further, there may be used inertgases such as nitrogen, carbon dioxide, nitrous oxide (N20) etc., whichare forced into the solution or dispersion under high pres sure and fromvacuoles upon release of the pressure. The volatile immiscible liquidsand gas-evolving materials such as sodium bicarbonate, usually requireheating of the mass for producing the foamy or inflated effect, whereaswhen methods utilizing the inert gases of the nitrous oxide type areused, heating is generally not essential to the production of a finalproduct having, throughout its cross-section, myriad small voids orpores forming a honeycomb or sponge-like structure. For example, anaqueous slurry of a water-insoluble dextran may be impregnated in aclosed container with nitrous oxide and as soon as the impregnatedmaterial is released, as through a hose nozzle, it immediately foamsand, on dr ing, a strong, soft sponge of homogeneous character andhaving fine interconnecting pores or cells is obtained.

Regardless of the foaming or inflating method employed, the final, driedproducts of the invention are firm, resilient structures comprisingcells defined by walls which do not tend to collapse during use of thesponge. The products can be cut to pieces of any desired size and shape.In some cases, for example when the dextran solution or dispersion isimpregnated with nitrous oxide or the like under pressure, theimpregnated mass may be cast directly to the size and shape of spongerequired, and having any predetermined thickness, by casting the mixtureof gas and solution or dispersion of the dextran directly from theimpregnating or mixing vessel into which the gas is introduced underpressure, into the cavity of an open mold having the predetermineddimensions.

The dextran or dextran conversion product may be mixed with an organicsolvent to obtain an essentially non-aqueous mass which is subjected tothe inflating or foaming treatment. Formamide and other lower acylamides, as well as the alkylated and dialkylated, specificallymethylated and dimethylated lower acyl amides, such as dimethylacetamideand dimethyl formamide, are examples of such solvents which may be usedin preparing the mass but other organic solvents may also be used andare selected so that they are readily evaporated from the inflated orfoamy mass during drying thereof. In general, it will be preferred todisperse or slurry the particulate water-insoluble dextran or dextranconversion product in water and bring the aqueous mass to the inflatedfoamed condition. Water-soluble dextrans or their water-solubleconversion products may be brought to the water-insoluble state afterthe foam is formed.

The following examples will illustrate specific embodiments of theinvention.

Example I A substantially pure, water-insoluble dextran in particulatecondition is mixed with water to produce a thick slurry. The slurry isimpregnated in a pressure cylinder equipped with an agitating devicewith nitrous oxide at from 80 to 250 lbs. pressure, with constantagitation of the mass to ensure thorough and uniform distribution of thegas in the slurry. The impregnated, expanded slurry is dischargedthrough a hose having a relatively small bore nozzle into an open moldto obtain a sponge-like mass of a shape and size corresponding to themold cavity. The expanded foam settles evenly into the mold cavity. Themolded or shaped foam is then dried by evaporation of the water. Thefirm, dried material, which is cellular in cross-section, can be die-cutto any shape or sliced, as desired.

Example 11 A water-soluble dextran is dissolved in a sufficient amountof water to produce a thick, creamy solution. Between 0.01% and 10.0%(on the weight of the dextran) of formalin (40% aqueous solution offormaldehyde) is added and the mixture is allowed to stand for about twohours, with warming, if desired. The mix is then placed in a vesselequipped with a heater and beaten vigorously until a firm foam isformed. The foam is placed on screens in a drying oven in which dry air(10% relative humidity) is circulated constantly. In order to expeditereaction of the formaldehyde and dextran to produce a water-insolubledextran formal, the dried foam is sprayed with a dilute aqueous solutionof sulfuric acid and heated at elevated temperature between 110 and 120C. until a substantial reaction product of the dextran and formaldehydeis produced. The insolubilized celluar material is then rinsed free ofacid, and dried.

Those dextran sponges which are intended for therapeutic use may bepackaged for marketing and may be sterilized before or after packaging.

The dextrans are ideally suited to use as therapeutic sponges. They arebland, stable, non-irritating materials which, in the pure condition,are non-toxic. They are heptanes and hence are immunologically activematerials which do not induce allergic reactions. The dextrans are notstored in body tissues and appear to be completely broken down in thebody, probably to glucose and apparently by enzyme action. The spongesmade from them can be inserted in incisions which are then closed,without damage. They have the additional advantage of a high liquidpick-up and retention capacity and when they are soaked in a therapeuticagent and then placed in an incision or in a body cavity, thetherapeutic agent is released to the area to be treated gradually, at amore or less controlled rate, and over a long period of time. Alsobecause of the high moisture pick-up and retention capacity of thedextrans, the sponges are particularly advantageous in taking up bloodaround an incision or the like, since they pick up and hold aconsiderable amount of blood without requiring frequent replacement. Thesponges may be pre-treated with a deodorant in order to neutralize orkill the odors caused by suppuration.

It will be understood that although the sponges in accordance with theinvention have been discussed in detail in connection with those whichare useful in the medical and surgical arts and particularly suited tosuch use by virtue of being readily absorbed in and assimilated byliving animal bodies, the sponges of the dextran conversion productswhich are not absorbed by living bodies may be used for any otherpurpose for which sponges are commonly employed, for example inhousehold applications.

Additional examples of dextran derivatives which may be treated asdescribed herein to produce a firm, stable foam include water-insolubleethers, esters, and etheresters such as are described in U. S. Patents2,203,7025, 2,229,941 and 2,236,386 to G. L. Stahly and W. W. Carlson,including benzyl dextran, dextran benzyl etherphthalyl ester, dextranbutyl ether-benzoyl ester, etc., lower fatty acid esters of dextran suchas dextran acetate, higher fatty acid esters of dextran and higher fattyacid esters of carboxyalkyl dextrans. Examples of waterinsoluble dextranderivatives suitable for use in making sponges adapted to therapeuticuse include such higher fatty esters as dextran palmitate and dextranlaurate and the palmitic and lauric acid esters of carboxymethyldextran. When the dextran is of the inherently water-soluble type, theester groups may be selected so that the esterified product is insolubleor substantially insoluble in water. When the sponge is intended fortherapeutic use, the dextran derivative is one which is physiologicallyinnocuous and readily and wholly absorbed in or assimilated by livinganimal bodies. Examples of such derivatives are the higher fatty acidesters such as dextran palmitate and dextran laurate containing, peranhydroglycopyranosidic group, an average of from less than 1.0 to 3.0palmityl or lauryl groups, and carboxymethyl dextran palmitates andlaurates in which the palmityl and lauryl groups predominate, i. e.,ether-esters containing an average of less than 1 to 1.0 carboxymethylgroup and from about 1.5 to 2.0 palmityl or lauryl groups. The dextranderivatives may be caused to foam and expand in the same manner as thedextrans. They may be dispersed in aqueous media or dissolved in asuitable solvent, prior to the inflating or foaming treatment. Forexample, benzyl dextran is 6 soluble in such solvents as acetone andethyl acetate, which may be used. 1

Various adjuvants may be mixed with the medium before the foamingtreatment, particularly when the sponge is intended for uses other thantherapeutic uses. Such adjuvants include pigments and other effectmaterials.

Various changes and modifications may be made in practicing theinvention without departing from its spirit and scope and it is to beunderstood, therefore, that I desire to comprehend within my inventionall such modifications as may be necessary to adapt it to varyingconditions and uses.

I claim:

1. A firm, water-permeable, substantially water-insoluble sponge-likeproduct consisting essentially of a porous mass of a substance selectedfrom the group consisting of dextra'ns and dextran conversion products,said mass having, in cross-section, a cellular, foam-like structure.

2. A firm, water-permeable, substantially watert-insoluble sponge-likeproduct consisting essentially of a porous mass of dextran, said masshaving, in cross-section, a cellular, foam-like structure.

3. A firm, water-permeable, substantially waterinsoluble sponge-likeproduct consisting essentially of a porous mass of a dextran conversionproduct, said mass having, in cross-section, a cellular, foam-likestructure.

4. A substantially water-insoluble therapeutic sponge consistingessentially of a sterile, porous mass of a substantially pure dextranabsorbable without deleterious effect by living bodies, said masshaving, in cross-section, a cellular, foam-like structure.

5. A substantially water-insoluble therapeutic sponge consistingessentially of a sterile porous mass of a substantially pure dextranconversion product absorbable without deleterious effect by livingbodies, said mass having, in cross-section, a cellular, foam-likestructure.

6. A firm, water-permeable, substantially water-insoluble sponge-likeproduct consisting essentially of a porous mass of a carboxymethyldextran, said mass having, in cross-section, a cellular, foam-likestructure.

7. A firm, water-permeable, substantially waterinsolu'nle sponge-likeproduct consisting essentially of a porous mass of a dextran ether, saidmass having, in cross-section, a cellular, foam-like structure.

8. A firm, water-permeable, substantially waterinsoluble sponge-likeproduct consisting essentially of a porous mass of a dextran ester, saidmass having, in cross-section, a cellular, foam-like structure.

9. A firm, water-permeable, substantially watersoluble sponge-likeproduct consisting essentially of a porous mass of a dextran higherfatty acid ester, said mass having, in cross-section, a cellular,foam-like structrue.

10. A firm, water-permeable, substantially waterinsolubie sponge-likeproduct consisting essentially of a porous mass of a dextran high fattyacid ester of carboxymethyl dextran, said mass having, in cross-section,a cellular, foam-like structure.

11. in a method of making a firm, water-permeable, substantiallywater-insoluble sponge-like product having, in cross-section, acellular, foam-like structure, the steps of (a) mixing a dispersion of asubstance selected from the group consisting of dextrans and dextranconversion products in a liquid which is chemically inert to the dextranand dextran conversion products with an inflating agent, (b) removingthe inflating agent to leave the mass in the form of a foam, and dryingthe inflated, cellular, foam-like mass of dextran or dextran conversionproduct remaining after removal of the inflating agent.

12. In a method of making a firm, water-permeable, substantiallyWater-insoluble sponge-like product having, in cross-section, acellular, foam-like structure, the steps 7 of (a) heating air into adispersion of a substance selected from the group consisting of dextransand dextran conversion products in a liquid which is chemically inert tothe dextran and dextran conversion products, until a firm foam isformed, and (b) drying the foam.

13. In a method of making a firm, water-permeable, substantiallywater-insoluble sponge-like product having, in cross-section, acellular, foam-like structure, the steps of (a) introducing a gas underpressure into a mass comprising a substance selected from the groupconsisting of clextrans and dextran derivatives dispersed in a liquidwhich is chemically inert to the dextran and dextran conversion productswhile agitating the mass, (b) abruptly releasing the pressure to causefoaming of the mass, and (c) drying the foamed mass.

14. A method according to claim 13 in which the gas is nitrous oxide.

15. A method of making a firm, water-permeable, substantialiyWater-insoluble sponge-like product having, in cross-section, acellular, foam-like structure, which comprises forming a thick slurry ofa particulate, substantially water-insoluble dextran in water, beatingair into the slurry until a foam is formed, and drying the foam.

16. A method of making a firm, shaped, waterpermeable, substantiallywater-insoluble sponge-like product having, in cross-section, a cellularfoam-like structure, which comprises introducing a gas under pressureinto a thick slurry of a particulate, water-insoluble dextran in water,while agitating the slurry, casting the mass containing the gas directlyinto an open mold to effect release of the gas and foaming of the mass,and drying the foam to obtain a product having substantially the shapeand size of the mold cavity.

References Cited in the file of this patent UNITED STATES PATENTS2,372,669 Heneyl et al. Apr. 3, 1945 2,418,211 Guilfoyle Apr. 1, 19472,461,746 Lathrop et al. Feb. 15, 1949 2,465,357 Correll Mar. 29, 19492,512,463 Maier June 20, 1950 2,613,189 Sarbach et a1. Oct. 7, 1952FOREIGN PATENTS 402,055 Great Britain Nov. 9, 1933 OTHER REFERENCESWhistler et al.; Polysaccharide Chemistry, Acadamic Press, Inc, New York(1953), pp. 66 and 375-382.

1. A FIRM, WATER-PERMEABLE, SUBSTANTIALLY WATER-INSOLUBLE SPONGE-LIKEPRODUCT CONSISTING ESENTIALLY OF A POROUS MASS OF A SUBSTANCE SELECTEDFROM THE GROUP CONSISTING OF DEXTRANS AND DETRAN CONVERSION PRODUCTS,SAID MASS HAVING, IN CROSS-SECTION, A CELLULAR, FOAM-LIKE STRUCTURE.